1. Field of the Invention
The present invention relates to a composition for forming an insulating film which is to be used for electronic devices and the like and is excellent in film properties such as dielectric constant and mechanical strength; and an electronic device having an insulating film obtained using the composition.
2. Description of the Related Art
In recent years, power consumption and delay time have increased because the progress of high integration, multifunction and high performance in the field of electronic materials has led to an increase in circuit resistance and condenser capacity between interconnects. Particularly, an increase of delay time becomes a large factor for the reduction of signal speed of devices and generation of crosstalk so that reduction of parasitic resistance and parasitic capacitance is required in order to reduce this delay time and accelerate the speed of devices. As one concrete measure for reducing this parasitic capacitance, an attempt has been made to cover the periphery of interconnects with a low-dielectric-constant interlayer insulating film. In addition, the interlayer insulating film is expected to have heat resistance high enough to withstand the thin film formation step at the time of producing a mount board and post steps such as chip connection and pin insertion and also chemical resistance high enough to withstand a wet process. Moreover, Al interconnects have recently been replaced by low resistance Cu interconnects and it is therefore common practice to carry out planarization by CMP (chemical mechanical polishing). The interlayer insulating film is therefore required to have mechanical resistance high enough to withstand this process.
Although polybenzoxazole and polyimide are widely known as materials for insulating films, insulating films obtained from them are not satisfactory from the viewpoints of low dielectric constant, low water absorption, durability and hydrolysis resistance because they contain a nitrogen atom having high polarity.
High heat-resistant resins having a polyarylene ether as a main chain are known. They have a dielectric constant falling within a range of from 2.6 to 2.7. In addition, a film obtained by crosslinking polymerization of a cage silsesquioxane having, in the molecule thereof, a plurality of carbon-carbon double bonds is proposed. It has a dielectric constant of from 3.3 to 3.5 (JP-A-2002-363414). A further reduction in a dielectric constant is desired in order to realize a high-speed device.
Use, as a precursor, of a dendrimer, which has an alkoxysilyl group at a branched chain end linked via an amide bond, for an insulating film while making use of a sol-gel reaction is proposed (JP-A-2002-338693). The insulating film thus obtained has however drawbacks such as high dielectric constant, poor heat resistance and high hygroscopic property.